The psychological thriller was one of the Clueless star's final projects before she suffered a fatal cardiac arrest on Sunday (20Dec09), aged just 32.
An autopsy was carried out on Monday (21Dec09) but the cause of death has yet to be determined.
Murphy's husband, British screenwriter Simon Monjack, insisted the actress had not been taking any dangerous drugs prior to her passing, but revealed she had been diagnosed with a non-life-threatening heart murmur and had battled laryngitis earlier this year (09).
Chambers admits he was concerned about Murphy's wellbeing during filming, but she assured him she was fine and completed the job with no problems.
He tells the Los Angeles Times, "She looked ill, as much as 10 pounds underweight, and she's a small person to begin with.
"She easily could have made an excuse not to come to work, but she didn't. She said, 'I've got to get better, but I want to do this part.'"
However, Murphy's designer pal Tiffany Saidnia insists the actress was in good health and she's struggling to accept the star is dead - because "there was nothing wrong with her".
Saidnia can't understand how the star could suddenly drop dead because she appeared perfectly healthy when she made her final public appearance at Saidnia's fashion party in Los Angeles on 3 December (09).
She tells Life & Style magazine, "I'm shocked by this news - there was nothing wrong with her.
"Brittany was such a sweetheart, I'm deeply saddened about this. She was such a sincere person and wanted the best for everyone around her. She's gone too soon."